/*
 * Copyright 2018-2019 The Apache Software Foundation
 * Modifications 2019 Orient Securities Co., Ltd.
 * Modifications 2019 BoCloud Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.orientsec.grpc.common.collect;



import java.util.AbstractSet;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * 支持同步的HashSet
 *
 * @author heiden
 * @since 2018/3/15.
 */
public class ConcurrentHashSet<E> extends AbstractSet<E> implements Set<E>, java.io.Serializable {

  private static final long serialVersionUID = -8672117787651310382L;

  private static final Object PRESENT = new Object();

  private final ConcurrentMap<E, Object> map;

  public ConcurrentHashSet() {
    map = new ConcurrentHashMap<E, Object>();
  }

  public ConcurrentHashSet(int initialCapacity) {
    map = new ConcurrentHashMap<E, Object>(initialCapacity);
  }

  /**
   * Returns an iterator over the elements in this set. The elements are
   * returned in no particular order.
   *
   * @return an Iterator over the elements in this set
   *
   */

  public Iterator<E> iterator() {
    return map.keySet().iterator();
  }

  /**
   * Returns the number of elements in this set (its cardinality).
   *
   * @return the number of elements in this set (its cardinality)
   */
  public int size() {
    return map.size();
  }

  /**
   * Returns <tt>true</tt> if this set contains no elements.
   *
   * @return <tt>true</tt> if this set contains no elements
   */
  public boolean isEmpty() {
    return map.isEmpty();
  }

  /**
   * Returns <tt>true</tt> if this set contains the specified element. More
   * formally, returns <tt>true</tt> if and only if this set contains an
   * element <tt>e</tt> such that
   * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
   *
   * @param o element whose presence in this set is to be tested
   * @return <tt>true</tt> if this set contains the specified element
   */
  public boolean contains(Object o) {
    return map.containsKey(o);
  }

  /**
   * Adds the specified element to this set if it is not already present. More
   * formally, adds the specified element <tt>e</tt> to this set if this set
   * contains no element <tt>e2</tt> such that
   * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>. If this
   * set already contains the element, the call leaves the set unchanged and
   * returns <tt>false</tt>.
   *
   * @param e element to be added to this set
   * @return <tt>true</tt> if this set did not already contain the specified
   * element
   */
  public boolean add(E e) {
    return map.put(e, PRESENT) == null;
  }

  /**
   * Removes the specified element from this set if it is present. More
   * formally, removes an element <tt>e</tt> such that
   * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>, if this
   * set contains such an element. Returns <tt>true</tt> if this set contained
   * the element (or equivalently, if this set changed as a result of the
   * call). (This set will not contain the element once the call returns.)
   *
   * @param o object to be removed from this set, if present
   * @return <tt>true</tt> if the set contained the specified element
   */
  public boolean remove(Object o) {
    return map.remove(o) == PRESENT;
  }

  /**
   * Removes all of the elements from this set. The set will be empty after
   * this call returns.
   */
  public void clear() {
    map.clear();
  }

}
